1. Field of the Invention
The present invention relates to a liquid cartridge. More particularly, the present invention relates to a liquid cartridge for accommodating liquid while maintaining a negative pressure by means of a differential pressure regulating valve and supplying the liquid to a liquid ejection head via a supply portion thereof while keeping a constant negative pressure.
2. Description of the Related Art
An ink cartridge for supplying ink while keeping the pressure at an ink supply port to be a negative pressure that does not allow leak of ink by using a pressure difference regulating valve is distributed while being packed in a sealed package under reduced pressure. Therefore, at the initial use of the ink cartridge, the pressure in an ink supply pass from the ink supply port to an ink accommodating chamber is kept lower than atmospheric pressure.
Thus, when new ink is supplied from the cartridge to an ink-jet head, that is an exemplary liquid ejection head, air bubbles that entered the ink-jet head or an ink-supply needle when the cartridge is detached or attached can be dissolved easily by the degassed ink supplied from the cartridge. This provides an advantage that ink ejection characteristics can be maintained whether the air bubbles entered or not.
On the other hand, at a time when the ink supply port of the cartridge is mounted onto the ink-supply needle, the negative pressure in the cartridge acts on the ink-jet head. Therefore, meniscus at a nozzle opening of the ink-jet head may be undesirably drawn toward the cartridge. This may adversely affect the ink-ejection characteristics.
Therefore, the ink cartridge mentioned above adopts a structure in which the ink accommodating chamber is released to ambient air before the ink-supply needle in communication with the liquid ejection head, i.e., the ink-jet head communicates with the ink supply port, as described in EP-A-1199179, for example.
However, this structure has a problem that an arrangement or design for opening an air valve and a position of an air valve are restricted and, thus, the structure of the holder or liquid emission cartridge becomes complicated.